Method of manufacturing a miniaturized three- dimensional electric component

ABSTRACT

Manufacturing of miniaturized three-dimensional electric components are presented, as well as components manufactured by the methods. The manufacturing methods comprise micro-replication of at least one master structure, e.g. via a mould structure, in at least one polymer layer onto which layer at least one conductive path is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is for entry into the U.S. national phase under §371for International Application No. PCT/SE02/00784 having an internationalfiling date of Apr. 22, 2002, and from which priority is claimed underall applicable sections of Title 35 of the United States Code including,but not limited to, Sections 120, 363 and 365(c), and which in turnclaims priority under 35 USC §119 to Swedish Patent Application No.0101378-8 filed on Apr. 20, 2001.

TECHNICAL FIELD

The present invention relates to methods for manufacturing miniaturizedelectric components, in particular manufacture of miniaturized electriccomponents having a substantially non-flat character with regard tospatial three-dimensional extension.

BACKGROUND

The technique of making small electric components suitable for use inproducts such as computers and telecommunication equipment has evolvedduring the last half century into a major branch of industry, producingever-smaller components. To name an example, the transistor has gonefrom being a centimeter-sized object in the early days of it'sdevelopment in the 1940's and 1950's to a sub-micrometer object today.

However, there are still obstacles to be overcome in the field ofminiaturisation of electric components. In particular, components thatrequire certain spatial properties, i.e. shape, are still difficult tominiaturise while still retaining optimal electric properties. Suchcomponents include inductors, transformers, capacitors etc.

Of course, there have been numerous attempts to produce these types ofminiaturized components. For example, three-dimensional micro-machinedinductors have been studied by several groups. The geometry of thestructures are typically solenoids. Examples of the state of the artinclude the work presented by J. B. Yoon et al., “Monolithic integrationof 3-D electroplated microstructures with unlimited number of levelsusing planarization with a sacrificial metallic mold”, IEEE MEMS-1999 aswell as U.S. Pat. No. 5,793,272, which shows an integrated toroidalinductor. U.S. Pat. No. 5,793,272 describes a toroidal coil produced bya dual-damascene process. A 1.4 nH coil produced by this processachieved a Q value of 40 at 5.8 GHz.

However, all these state of the art integrated inductors for radiofrequency application are based on a planar geometry. The limitations ofplanar integrated coils are several and include that the Q value of theinductor is limited by self-resonance due to the parasitic capacitanceof the coil through capacitive coupling to the substrate. Also the ratioof the inductance and series resistance is not optimal. Secondly, themagnetic field of the inductor couples to the surrounding electronics.Hence, interference with other parts of the electronics limits thedensity of inductive components on the chip.

Moreover, planar inductors with high Q values are large in terms ofsilicon surface area, an area that cannot be utilised for any otherpurpose.

SUMMARY OF THE INVENTION

It is hence an object of the present invention to solve a problem of howto obtain miniaturized electric components having a substantiallynon-flat character with regard to spatial three-dimensional extension.

In its most general aspect the present invention solves the problem inthat it provides a method for manufacturing a miniaturizedthree-dimensional electric component. The manufacturing method comprisesmicro replication of at least one master structure. The replicationtakes place via a mould structure, e.g. an insert, or a templatestructure, in at least one polymer layer onto which layer at least oneconductive path is provided.

An advantage of the invention in relation to prior art methods formanufacturing miniaturized electric components lies in the fact that thecomponent is realised in a polymer material, as opposed to prior arttechniques of utilising, e.g. Silicon wafers Polymer materials can beformed into more or less arbitrary shapes by casting or by injectionmoulding or embossing.

Particularly advantageous is the use of the method of the presentinvention when manufacturing electric inductors, and most notably,arrays of inductors, for use in e.g. small hand held radio devices suchas mobile communication terminals. In such devices there is a need foranalogue filters, resonators and matching circuits in which LC-circuitsare necessary. In such circuits there is an inherent need for inductorshaving high Q-values, as will be discussed in some detail below inconnection is with a preferred embodiment of the invention.

Another advantage obtained by the use of polymers to create small-scalecomponents relies on the simple fact that a polymer layer can be used tobuffer the thermal expansion mismatch between different layers. Thecomponents manufactured by the present inventive method become extremelycompact and hence are capable of being located in close proximity toother circuitry that may generate more or less heat and hence createconditions for differential expansion of substrates etc. Polymers areusually poor heat conductors and hence the use of polymers tomanufacture the components enables a user to design circuitry whereheat-emitting components may be located more or less close to heatsensitive components.

In a first preferred embodiment of the invention, the method is realisedin a number of processing steps defining a more or less directmanufacture of a component from a master structure carrying all therequired three-dimensional geometry of the component. The methodaccording to the first embodiment comprises the processing steps ofcopying the master structure to create a mould structure, e.g. aninsert. The mould structure is then used in turn to replicate the masterstructure in a first and second polymer layer. Polymer supportstructures are hence obtained.

A first conductive path and a second conductive path are then providedonto the respective first and second polymer layers. The two polymerlayers are then joined, thereby obtaining the electric component.Alternatively, the conductive path may be provided after joining thepolymer layers.

As will be discussed further below, the polymer layers and theconductive paths may be obtained by a number of different methods.

In a second preferred embodiment of the invention, the method isrealised in a number of processing steps defining manufacture of acomponent from a master structure carrying the requiredthree-dimensional geometry of the component in a slightly differentmanner where the master structure is replicated into a templatestructure for the component to be. The method according to the secondembodiment comprises the processing steps of providing a firstconductive path and a second conductive path onto a respective first andsecond template structure. A first polymer layer and a second polymerlayer are provided onto the respective first and second templatestructures, thereby replicating the respective master structures in therespective polymer layers. This results in a first and second polymerlayer, i.e. a structure, joined to the respective first and secondconductive path. The first and second template structures are thenseparated from the respective first and second polymer layers and thetwo polymer layers are then joined, thereby obtaining the electriccomponent.

It is to be noted that the first and the second template structure maybe one and the same template structure which is used as the firsttemplate structure in an initial polymer layer creation sequence, and ina second sequence as the second template structure.

In a third preferred embodiment of the invention, the method is realisedin a number of processing steps defining manufacture of a component froma master structure. In this embodiment a first polymer layer, i.e. astructure, having a conductive path may be obtained either via a more orless direct manufacturing method as discussed in connection with thefirst embodiment, or as in the second embodiment where a template actsas a support firstly for the conductive path and subsequently thepolymer layer. The method according to the third embodiment then furthercomprises the processing steps of providing a sacrificial structure ontothe conductive path on the polymer layer structure already obtained. Asecond conductive path is then provided onto the sacrificial structure,whereupon the sacrificial structure can be removed, thereby obtainingthe electric component. However, it is not necessary to remove thesacrificial structure.

As in the first preferred embodiment of the invention, in these secondand third embodiments the polymer layers and the conductive paths may beobtained by a number of different methods, as will be discussed furtherbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a top view of a toroidal inductormanufactured according to the present invention.

FIG. 2 a-2 d shows schematically cross sectional views of substratesduring different stages of a first embodiment of a manufacturing methodaccording to the present invention.

FIG. 3 shows schematically a cross sectional view of a substratecomprising a ferromagnetic core.

FIG. 4 a-4 c shows schematically cross sectional views of substratesduring different stages of a second embodiment of a manufacturing methodaccording to the present invention.

FIG. 5 a-5 c shows schematically cross sectional views of substratesduring different stages of a third embodiment of a manufacturing methodaccording to the present invention.

FIGS. 6 a-d shows schematically cross sectional views of circuitscomprising an inductor according to the present invention.

FIG. 7 shows schematically a cross sectional view of a circuitcomprising an inductor according to the present invention.

FIG. 8 shows schematically a cross sectional view of a circuitcomprising an inductor according to the present invention.

FIG. 9 shows a diagram of Q-values for inductors.

PREFERRED EMBODIMENTS

The invention in its general form, as discussed above, is related tomanufacture of any electric component. In the description to followbelow, a number of embodiments of a manufacturing method will bepresented. Common to the embodiments is the choice of a toroidalinductor, i.e. a toroidal coil, as representing the electric componentto be manufactured. Small-scale inductors are required in many kinds ofproducts, not least in the field of small hand-held devices such asmobile telephone terminals containing high frequency radio transmittersand receivers as well as transformers and baluns. FIG. 1 shows a topview of a toroidal inductor, as it would appear if exposed. As will beshown, however, the toroidal coils manufactured according to theinventive method will after the last step of manufacture be enclosed bya polymer material and not be visible to inspection such as FIG. 1suggests. The coil of FIG. 1 comprises a torus shaped conductive path101 having connecting ends 102,103. A typical size of such a componentis on the order of 10² μm.

The embodiments of the manufacturing method will be presented by use ofschematic figures of such an enlarged scale that only one component,i.e. toroidal coil, is visible in each figure. However, it shall bestressed that, when utilising the manufacturing method according to theinvention, machinery suitable for manufacturing, e.g., optical discssuch as CD or DVD is a preferred choice. As the skilled person willappreciate, the use of such machinery entails producing polymer layerssuitable for manufacturing a plurality of components simultaneously.

Three preferred embodiments of the invention will be disclosed withreference to cross sectional views in FIGS. 2-6. The cross sectionalviews may, e.g., be the AA-section indicated in FIG. 1. Each embodimentrequires a pre-fabricated original or master, which contains therequired three-dimensional geometrical features of the final structureof the components. It is assumed that fabrication of the original ormaster is known to the skilled person and that the skilled person willselect the most appropriate method amongst available methods for siliconmicromachining.

Referring now to FIGS. 2 a-2 c, a first embodiment of an inventivemanufacturing method will be described. Initially a mould structure orinsert 203 is created from the master structure. The mould insert 203 isobtained by electroforming the master, which entails depositing a metalseed-layer onto the master structure, electroplating a thick layer ofmetal, separating the mould insert 203 from the master and planarisingthe backside of the mould insert.

The master structure is then replicated by one of three methods.Replication by casting is initiated by forming a cavity between themould insert 203 and a substrate 202 which is filled with a suitablepolymer material 201, thus replicating the master structure.

Alternatively, the master structure may be replicated by injectionmoulding or embossing in a suitable polymer.

The mould insert 203 holds the three-dimensional geometry of the finalcomponent, i.e. a toroidal coil in the example discussed here, andcomprises a semi-torus 204 and a via core structure 205. The substrate202 on which the polymer layer is provided is preferably part of anelectric circuit (not shown) with which the toroidal coil is to beconnected by means of a via obtained by the via core structure 205 and acontact pad 230.

After replication by the chosen method, the polymer layer 201 ismetallised with a thin conductive layer 206. The thin conductive layer206 is used as an electrode in a process for application of photoresistby electrodeposition. Electrodeposition provides a conformal coating ofphotoresist 207 over the three-dimensional geometry of the polymer layer201. The photoresist 207 is then patterned by methods known to thoseskilled in the art.

The patterning will entail providing a side-wall pattern for theconductive parts of the component and, as illustrated in FIG. 1, providethe coil with the conductive path 101 as well as the connecting ends102,103.

Preferably, the conductive path is provided by electroplating orelectroless plating a suitable metal onto the patterned polymer layer201 prior to joining of the first and second layers. However, theconductive path may be provided by internal plating after joining of thepolymer layers. A suitable metal will be selected by the skilled personwhen using the inventive method.

After provision of the conductive path, the photoresist is removed andthe seed layer etched away by methods known in the art to provideseparate conductive paths 208.

Referring now to FIG. 2 d, in which is shown a first and a secondstructure halve 241,242 comprising substrates 202,222 polymer layers201,221 and conductive paths 208,228 having been subject to theprocessing steps discussed above in connection with FIGS. 2 a-2 c. Thesecond structure 242 is aligned with respect to the first structure 241using visual and mechanical systems that are outside the scope of thepresent invention. FIG. 2 d also illustrates a finalised component 240comprising the two joined structure halves 241,242 created by the methodas disclosed above.

Normally, plating of the conductive paths 208,228 is performed prior tothe joining of the two halves 241,241 and a conducting joint may beachieved by thermocompression bonding or by a short period ofelectroless or electrolytic internal plating.

FIG. 3 illustrates schematically a step of toroidal coil manufacturingprior to joining of two halves 341,342 similar to the halves 241,242 inFIG. 2 d. On top of substrates 302,322 are respective polymer supportstructures 301,321 and provided with a ferromagnetic core 304.

In low frequency applications, attempts have been made to solve theproblem of creating integrated inductors by micro-machining ofcomponents. The requirement of low frequency applications is that theinductance value of the coil should be in the range of micro Henrys. Inorder to create such high inductance values the core of the coil shouldbe filled by some ferromagnetic material. FIG. 3 shows that a toroidalcoil manufactured according to the invention can be provided with aferromagnetic core 304 during the process of joining the two halves341,341.

An alternative way of obtaining a ferromagnetic core of the coil is tofill the interior of the finished coil with ferromagnetic particles viafluid channels provided for internal plating of the conductive layer, asdiscussed above. This can be done with the help of a carrier liquid thatsolidifies at, e.g., room temperature.

A second embodiment of the inventive method will now be described withreference to FIGS. 4 a-4 c. As in the, more or less, direct method ofreplication discussed above in connection with FIGS. 2 a-2 d, a masterstructure is needed in this second embodiment. However, in contrast tothe previously described embodiment, here the master structure isinitially replicated into one or more template structures 401. Such atemplate structure 401 acts as a platform for a conductive layer 407.The template structure 401 is metallised with a seed-layer 402 andpatterned as described in conjunction with the first embodiment. Theside-wall pattern is subsequently electroplated or electroless plated toprovide the conductive layer 407.

A polymer support structure 403 is then deposited onto the platedconductive layer 407, as illustrated in FIG. 4 b. This deposition ofpolymer 403 may be obtained by way of any of the processes as discussedin connection with FIGS. 2 a and 2 b. The deposition of the polymerlayer 403 results in a joining of the plated conductive layer 407 andthe polymer support structure 403.

The template structure 401 and the polymer support structure 403 arethen separated resulting, as is illustrated in FIG. 4 c, in a substratecomprising the conductive path of a toroidal coil 404 and a via corestructure 405 supported by the polymer support structure 403. Furthermanufacture of a complete toroidal coil is then performed according tothe steps described in the first embodiment. Needless to say, one andthe same template may be used to manufacture a plurality of polymerstructures.

A third embodiment of the inventive method will now be described withreference to FIGS. 5 a-5 c. A polymer support structure 501 comprising aconductive path 507 is obtained by way of any of the manufacturingmethods according to the first or second embodiment discussed above.

A layer of photoresist 503 is deposited onto the polymer supportstructure 501 and the conductive layer 507 by way of any known techniquesuch as spin coating, spray coating, electrodeposition or possiblycasting. All areas except a torus shaped area 504 on top of theconductive layer 507 of the coil is removed by way of exposure anddevelopment according to known art, as illustrated in FIG. 5 b. Theremaining photo resist is heated leading to a flowing and reshaping ofthe resist into a more or less rounded torus of photo resist 505, asillustrated in FIG. 5 c.

A seed-layer is then provided onto the sacrificial layer and patternedas described above in connection with the first and second embodiments.Electroplating or electroless plating then provides the conductive pathto complete the component.

The embodiments of manufacturing methods described above may be used tomanufacture a number of different miniaturized electric components andcircuitry comprising a plurality of such components.

Stand-alone components and systems as exemplified in FIG. 1 includeinductors, arrays of inductors, transformers and arrays of transformers,differing in the way in which the conductive paths, and connections tothe paths, are arranged. In FIGS. 6 a-6 d is shown an electricstand-alone component 600 placed on a multichip module carrier substrate601 and encapsulated in a polymer support structure 602 In FIG. 6 a, thestand-alone component is, together with other RF circuitry 604, furtherembedded in a protective polymer encapsulation 603.

In FIG. 6 b, the stand-alone component 600 is underfilled with aprotective polymer layer 605 instead of being encapsulated.

In FIG. 6 c, the component is a stand-alone component placed, togetherwith other RF circuitry 604, on a printed wiring board 606 andencapsulated in a polymer support structure 602.

In FIG. 6 d, the inventive component 607 is part of a 3-dimensionalstacked multichip module 608 on a printed circuit board 604, includingother stacked RF circuitry 609 and 610, including various RF, MEMS,processor and memory devices.

In FIG. 7, the components 612 according to the invention are embedded ina multichip 614 module carrier substrate 611. The multichip modules 614may be encapsulated 613 and the carrier substrate 611 provided withflip-chip solder bumps 615. Of course any appropriate bonding techniquecan be used.

In FIG. 8, the components 616 according to the invention are is embeddedin a protective polymer encapsulation 617 above a multichip module 619carrier substrate 618.

Naturally, the components may also be manufactured such that a carrierpolymer substrate contains, apart from the embedded inductor coils, alsothe vias and interconnecting wires.

Although the components that may be manufactured in accordance with theinvention include capacitors, resistors and simple electrodes, it isforeseen that miniature inductive components will be a major area ofapplication, not least due to the fact that prior art miniaturizedinductors have lower Q-values. In comparison with prior-art devices suchas the devices of U.S. Pat. No. 5,793,272, the cross-section of thetorus that determines the Q value can be made much larger. Using theexpression for the Q-value for a toroidal inductor:

$Q_{m} = {\sqrt{\frac{\mu_{0}}{{\pi\rho}_{Cu}}} \cdot \frac{\sqrt{f} \cdot r_{lorus} \cdot \left( {{4\pi\; R_{coil}} - {2 \cdot N \cdot s_{coil}}} \right)}{2R_{coil}}}$and inserting values for the parameters for Copper and Gold, the diagramof FIG. 9 is obtained. In the diagram of FIG. 9, the Q-value is plottedas a function of outer diameter of the toroidal coil with electroplatedcopper conductors (circles) or electroplated gold conductors (squares).For comparison, data for a state-of-the-art optimised planar coil oninsulating substrate with 8 μm gold conductors are included (triangles).

From the diagram of FIG. 9 it can be seen that, for a similar coildiameter, the Q-value is more than twice as large for a toroidalinductor manufactured in accordance with the invention, as compared witha state-of-the-art inductor.

Additional advantages of a toroidal inductor become apparent whenconsidering the interference of the radio frequency signals of the coilwith other electronics in it's vicinity. The interference is minimalbecause the field is concentrated inside the torus with very smallleakage and with very small guard. Thus the toroidal coil can be placedon top of active circuitry. Moreover, no area on top of the circuitry islost hence allowing for a more compact mechanical design.

1. A method for manufacturing a miniaturized three-dimensional electriccomponent comprising: micro replicating at least one master structure inat least a first polymer layer and a second polymer layer so as to format least one mould structure in the respective first and second polymerlayers, thereby obtaining a first polymer support structure and a secondpolymer support structure, providing a first conductive path and asecond conductive path onto the respective first and second polymersupport structures, wherein said first and second conductive paths atleast partly comprise electroplating, and joining the first and secondpolymer support structures, thereby obtaining the electric component,wherein electroplating of the first and second polymer supportstructures precedes the joining of the first and second polymer supportstructures and wherein electric connection between the first and secondconductive paths on the first and second support structures is securedby way of electroless plating.
 2. A method according to claim 1, whereinthe replication of the at least one mould structure precedes theproviding of the first conductive path and the second conductive pathonto the respective first and second polymer support structures which inturn precedes the joining of the first and second polymer supportstructures.
 3. A method according to claim 1, wherein the replication ofthe at least one mould structure precedes the joining of the first andsecond polymer support structures which in turn precedes the providingof the first conductive path and the second conductive path onto therespective first and second polymer support structures.
 4. A methodaccording to claim 1, wherein the replication of the mould structurecomprises embossing.
 5. A method according to claim 1, wherein thereplication of the mould structure comprises casting.
 6. A methodaccording to claim 1, wherein the replication of the mould structurecomprises injection moulding.
 7. A method according to claim 1, whereinthe providing of the first and second conductive paths at least partlycomprises electroless plating.
 8. A method according to claim 1,comprising providing a plating seed-layer prior to plating of the firstand second conductive paths.
 9. A method according to claim 8, whereinthe seed-layer is patterned by use of an electrodeposited photoresist toprovide a side-wall pattern prior to plating the first and secondconductive paths.
 10. A method according to claim 1, wherein the joiningof the first and second polymer support structures comprisesthermocompression.
 11. A method according to claim 1, comprising:replicating the at least one master structure into at least one templatestructure, providing a first conductive path and a second conductivepath onto a respective first and second template structure, providing afirst polymer layer and a second polymer layer onto the respective firstand second template structures, thereby replicating the respectivemaster structures in the respective polymer layers resulting in a firstand second polymer support structure joined to the respective first andsecond conductive path, separating the first and second templatestructure from the respective first and second polymer supportstructure, and joining the two polymer support structures, therebyobtaining the electric component.
 12. A method according to claim 11,wherein the provision of the polymer layers comprises embossing.
 13. Amethod according to claim 11, wherein the provision of the polymerlayers comprises casting.
 14. A method according to claim 11, whereinthe provision of the polymer layers comprises injection moulding.
 15. Amethod according to claim 11, wherein the provision of conductive pathsat least partly comprises electroplating.
 16. A method according toclaim 15, wherein electric connection between the conductive paths onthe support structures is secured by way of electroless platingsubsequent to the joining of the support structures.
 17. A methodaccording to claim 15, comprising providing a plating seed layer priorto plating of the conductive paths.
 18. A method according to claim 11,wherein the provision of conductive paths at least partly compriseselectroless plating.
 19. A method according to claim 11, wherein theseed-layer is patterned by use of an electrodeposited photoresist toprovide a side-wall pattern prior to plating the conductive paths.
 20. Amethod according to claim 11, wherein the joining comprisesthermocompression.
 21. A method according to claim 1, comprising:copying the at least one master structure into a mould structure,replicating the mould structure in a first polymer layer therebyobtaining a first polymer support structure, providing a firstconductive path onto the first polymer support structure, providing asacrificial structure onto the conductive path on the first polymersupport structure, and providing a second conductive path onto thesacrificial structure, thereby obtaining the electric component.
 22. Amethod according to claim 21, comprising: removing the sacrificialstructure.
 23. A method according to claim 21, wherein the provision ofthe polymer layers comprises embossing.
 24. A method according to claim21, wherein the provision of the polymer layers comprises casting.
 25. Amethod according to claim 21, wherein the provision of the polymerlayers comprises injection moulding.
 26. A method according to claim 21,wherein the provision of conductive paths at least partly compriseselectroplating.
 27. A method according to claim 26, comprising providinga plating seed layer prior to plating of the conductive paths.
 28. Amethod according to claim 21, wherein the provision of conductive pathsat least partly comprises electroless plating.
 29. A method according toclaim 21, wherein the seed-layer is patterned by use of anelectrodeposited photoresist to provide a side-wall pattern prior toplating the conductive paths.
 30. A method according to claim 1,comprising: replicating the at least one master structure into atemplate structure, providing a first conductive path onto the templatestructure, providing a first polymer layer onto the template structure,thereby replicating the master structure in the polymer layer resultingin a first polymer support structure joined to the first conductivepath, separating the template structure from the first polymer supportstructure, providing a sacrificial structure onto the conductive path onthe first polymer support structure, and providing a second conductivepath onto the sacrificial structure, thereby obtaining the electriccomponent.
 31. A method according to claim 30, comprising: removing thesacrificial structure.
 32. A method according to claim 30, wherein theprovision of the polymer layers comprises embossing.
 33. A methodaccording to claim 30, wherein the provision of the polymer layerscomprises casting.
 34. A method according to claim 30, wherein theprovision of the polymer layers comprises injection moulding.
 35. Amethod according to claim 30, wherein the provision of conductive pathsat least partly comprises electroplating.
 36. A method according toclaim 35, comprising providing a plating seed layer prior to plating ofthe conductive paths.
 37. A method according to claim 30, wherein theprovision of conductive paths at least partly comprises electrolessplating.
 38. A method according to claim 30, wherein the seed-layer ispatterned by use of an electrodeposited photoresist to provide aside-wall pattern prior to plating the conductive paths.
 39. A methodaccording to claim 1, wherein the miniaturized three-dimensionalelectric component is a miniaturized toroidal inductor coil.
 40. Amethod according to claim 39, comprising providing the toroidal coilwith a ferromagnetic core.
 41. A method according to claim 40, whereinthe providing of a ferromagnetic core is performed at least partly byproviding a solid ferromagnetic core.
 42. A method according to claim40, wherein the providing of a ferromagnetic core is performed at leastpartly by way of injection of ferromagnetic material.